YES! Waiting for processing to complete. Current status: Accepted................. Processing complete id: 9999999-b078-4a91-8a55-9999999 status: Accepted The issue in my case were the binaries sprinkled across all of the package. After I moved everything to Contents/MacOS as outlined in the above link the notarization is now succeeding. Thanks for your pointers, @DTS Engineer!

From https://developer.apple.com/documentation/xcode/embedding-nonstandard-code-structures-in-a-bundle: In some cases you need to work with nonstandard code structures, that is, code whose structure doesn’t match the standard bundle structure for your platform. For example, you might be building a Mac app and want to embed an open source language runtime in it. Yep, that's me 🙈.

Thanks @DTS Engineer for your response and links. I used plutil to validate my entitlements file. And it said OK. But as @Etresoft suggested I ended up adding more and more flags, until I had added about every flag I could find (eg. from https://developer.apple.com/documentation/security/hardened-runtime). Alas, it didn't help. I think what I'm struggling with is https://developer.apple.com/documentation/xcode/embedding-nonstandard-code-structures-in-a-bundle. I'll have to give that a closer look. All my Perl modules and helper binaries certainly aren't in standard locations.